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CO2-Responsive CCT Protein (CRCT) is a transcription factor regulating the expression of starch synthesis-related genes in the vegetative organs of rice. Among six rice cultivars (Nipponbare, Koshihikari, Habataki, Takanari, Momiroman, Leafstar), the expression of CRCT was highly correlated with the starch content of leaf sheath in Nipponbare, but not in Koshihikari, Takanari and Momiroman during plant development. Meanwhile, the expressions of starch synthesis-related genes such as ADP-glucose pyrophosphorylase large subunit 1 was correlated with CRCT expression in Nipponbare, Momiroman, and Leafstar, but the correlations were ambiguous in Koshihikari, Habataki, and Takanari. In addition, the slopes of its regression lines in Nipponbare were larger than those cultivars. These results suggest that the influence of CRCT on starch synthesis varies among these cultivars. Additionally, the similar cultivar differences were observed when these gene expressions were analyzed after sucrose treatment in leaf blade. Some mutations in the promoter regions of the starch synthesis-related genes were identified among these cultivars. There were cultivars in which the presence of mutations correlated with decreased expression of starch synthesis genes in response to CRCT. Thus, these mutations can partially explain the responsiveness of the starch synthesis-related genes to CRCT, and difference in starch content of vegetative organs among rice cultivars.